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Starfish13
1040218.  Tue Dec 10, 2013 7:05 am Reply with quote

Back to lead; sounding (measuring the depth) of given points in a body of water was carried out using a lead line. A lead line, also called a sounding line, is a long length of thin rope attached to a plumb-bob, usually, but not always, made of lead. The depth was originally calculated by pulling in the line and measuring lengths between outstretched arms, which approximately gives a fathom (6 feet). Although the rest of the world has standardised measurements of depth on nautical charts to be in metres, NOAA in the USA still gives bathymetric data in fathoms and feet.

Often a wad of tallow was fixed to the bottom of the plumb-bob, to sample the substrate comprising the bottom sediment. Silt, sand, shells and gravels would stick to the tallow, whereas clean tallow would indicate the seabed was rocky. As well as just being quite interesting, this was useful information for navigation/position fixing, pilotage and anchoring.

Although the use of lead lines in measuring depth has been replaced by echo sounding/sonar, often giving more accurate readings, the information on bottom type gathered in this way still features on nautical charts.

 
Efros
1040219.  Tue Dec 10, 2013 7:12 am Reply with quote

The act of sounding using a lead line gave rise to the naval expression of "swinging the lead", i.e. doing bugger all.

 
knightmare
1040225.  Tue Dec 10, 2013 7:44 am Reply with quote

There are 22 known metals heavier than lead: technetium, thorium, thallium, palladium, rhodium, ruthenium, berkelium, hafnium, curium, mercury, americium, californium, protactinium, tantalum, uranium, tungsten, gold, plutonium, neptunium, rhenium, osmium and iridium.

 
Efros
1040248.  Tue Dec 10, 2013 8:38 am Reply with quote

denser please.

 
knightmare
1040251.  Tue Dec 10, 2013 8:49 am Reply with quote

Quote:
denser please.


Sure...

Tc, Th, Tl, Pd, Rh, Ru, Bk, Hf, Cm, Hg, Am, Cf, Pa, Ta, U, W, Au, Pu, Np, Re, Os & Ir.

 
Efros
1040322.  Tue Dec 10, 2013 2:35 pm Reply with quote

Platinum?

 
knightmare
1040328.  Tue Dec 10, 2013 2:59 pm Reply with quote

Not in my book. But we've got a pencil to solve that, by adding Pt to the list: 23 metals.

 
PDR
1040355.  Tue Dec 10, 2013 5:26 pm Reply with quote

Starfish13 wrote:
Although the rest of the world has standardised measurements of depth on nautical charts to be in metres, NOAA in the USA still gives bathymetric data in fathoms and feet.


Back in the 80s I saw a soviet military map of the north coast of scotland. This showed terrain spot-heights in metres, but the litoral depths in fathoms which I found quite amusing at the time (no? I guess you had to have been there).

Quote:

Although the use of lead lines in measuring depth has been replaced by echo sounding/sonar, often giving more accurate readings, the information on bottom type gathered in this way still features on nautical charts.


I would actually suggest that the lead-line depths are probably *more* accurate (especially those taken from stationary surveying ships). Sonar is notoriously inaccurate in the vertical plane unless you can triangulate from multiple sources, because the speed and direction of the sound pulses varies with changes of depth, salinity, temperature, flow speed and direction, phase of the moon and local mermaid diet. Unlike Radar, the actual "sensor" end of a sonar system is almost useless without extensive post-processing using stochastic correlation techniques (that's a technical term for "guessing").

PDR

 
Starfish13
1040526.  Wed Dec 11, 2013 9:33 am Reply with quote

PDR wrote:
I would actually suggest that the lead-line depths are probably *more* accurate (especially those taken from stationary surveying ships). Sonar is notoriously inaccurate in the vertical plane unless you can triangulate from multiple sources, because the speed and direction of the sound pulses varies with changes of depth, salinity, temperature, flow speed and direction, phase of the moon and local mermaid diet. Unlike Radar, the actual "sensor" end of a sonar system is almost useless without extensive post-processing using stochastic correlation techniques (that's a technical term for "guessing").

PDR


I never though about those kind of factors affecting the result; I thought that improved accuracy might have been a result of side-scan sonar creating a 3Dimage of the sea-floor, as opposed to a series of single measurements with a lead line that are effectively "stabbing in the dark". I suppose that "true" might be a better word than "accurate", in giving a picture of the seabed.

 
PDR
1040529.  Wed Dec 11, 2013 10:18 am Reply with quote

Even high-frequency sonars only really give "illustrative" pictures over any great change in depth. The speed of sound varies significantly wirth pressure, temperature, salinity etc, and water flows cause parallax errors as well.

A towed side-scan vehicle like the Gloria system (which I worked on in the early 80s) gives good results at short ranges because the vehicle is at a similar depth to the subject - you couldn't expect decent results from the surface.

The water conditions cause two problems - firstly they make the range data inaccurate due to variable speed of sound. Secondly the variation in SoS with depth effectively "bends the beam" causing image distorsion like a circus mirror. Conventional ship sonar suffers this, and there is a range beyond which the sound pulse heads down to the sea-bed and back as a result. Within this zone there is a complete sonar blind region before the pulse returns to the mid-water. So the sonar will provide coverage of the "direct path" region, then have a blind spot, then have another region of coverage (called the 1st convergence zone) and so on. Military passive sonars can often detect signals from the 3rd or 4th convergence zone, and whales are known to be able to communicate 10-20 convergence zones apart.

Radar doesn't suffer these problems to anything like the same extent partly because its a transverse wave (ie a wave that doesn't use the medium fopr propagation) but mainly because the ration of the speed of light to the speed of interfering phenmona is much larger than it is for sonar, although "gravity lensing aberation" is a similar kind of effect that afflicts passive radars (or radiotelescopes as they are otherwise known).

PDR

 
chrisboote
1040602.  Wed Dec 11, 2013 2:42 pm Reply with quote

PDR wrote:
Starfish13 wrote:
Although the rest of the world has standardised measurements of depth on nautical charts to be in metres, NOAA in the USA still gives bathymetric data in fathoms and feet.


Back in the 80s I saw a soviet military map of the north coast of scotland. This showed terrain spot-heights in metres, but the litoral depths in fathoms which I found quite amusing at the time (no? I guess you had to have been there).


Recently had an extension built onto our house
I did the structural plans. For the foundations, I have to measure the widths in feet and the depths in metres, due to pre/post 1994 legislation

 
ERose90
1040952.  Thu Dec 12, 2013 10:57 pm Reply with quote

Efros wrote:
Densities of gold, uranium and plutonium are all about twice that of lead. If you had handled (heh) any of them then the chances of being duped by lead would be remote I think.

Not saying there's an exact mass-to-mass ratio of lead to uranium, but it seems very likely that something as abundant as lead could be used in trickery of some sorts.

Here's a picture of the briefcase i mentioned.

Link to picture removed for tasteless content, not as described. QIM.

Under the grey padding its revealed there are lead bricks giving the weight, because the uranium container inside the case was itself empty. Just to give you a picture of what i'm suggesting. A more famous form of this trickery would be phone-books under a few stacks of money, in hopes the person would just take it without checking. I'm sure there must be records of something like this actually happening; movies can be quite silly but lets be honest, humans aren't the brightest.

 
Efros
1040999.  Fri Dec 13, 2013 4:18 am Reply with quote

That may have been a link to a briefcase once upon a time, it certainly isn't now.

 
julesies
1063670.  Sun Mar 16, 2014 9:48 am Reply with quote

Lead glass

 
mikeholden
1125109.  Sun Mar 22, 2015 9:02 pm Reply with quote

Alfred E Neuman wrote:
knightmare wrote:
And a directory is a yellow desktop folder, even if everybody would use the word folder to describe this icon.


As far as computers go, "folder" is a synonym for "directory" and the two terms can be used interchangeably. In DOS and if memory serves up to about Windows 3, they were called directories, and from Win95 on were called folders.

If you use a command prompt on a windows machine, the command to create a new folder is "md" which is short for "mkdir" which in turn is a contraction of "make directory".

Not everybody uses the word folder, some of us still use directory from time to time, not because we're being difficult, but because it's ingrained.


The term "directory" predates Windows (of any version) by quite some way. The term, and indeed the "mkdir" command you mention, come from the Unix operating systems that had been around for quite a while before Windows came on the scene.

As mentioned elsewhere, "folder" comes from a way of trying to make the whole thing more analogous to an office environment more suited to the less techy people who would be using it.

 

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